A good initial hypothesis would quickly dismiss inadequate structural engineering design as the cause of the roof collapse. The structure is likely to be simple in the extreme: Structural concrete slabs supported by regularly spaced columns bearing on concrete footings on good foundation soil.
If design had been inadequate the mall might have collapsed long ago. The “loads” (see below) in a simple building are easy for structural engineers to calculate and provide for.
Professional engineers are not infallible but we are governed by professional bodies that do watch us closely. We carry out our designs according to well understood principles and are held to a strict code of ethics. Cost is a factor in design; designs must be economical, but not at the expense of safety.
It’s sometimes another matter, however, once the construction drawings leave the design office. Design can be all well and good but construction inspection is sometimes left wanting.
The pressure on design engineers – not much really, is applying fairly simple design principles in providing for support of the structure, for a reasonable fee. The pressure on builders – quite a lot of pressue, actually, is getting the structure erected as quickly as possible, for the lowest price. The pressure on the inspector is ensuring the design is implemented properly, sometimes for a reasonable fee and sometimes with experienced, full time inspection, but not always. Construction inspection sometimes gets the short end of the stick as far as being adequately funded and staffed.
Inadequate inspection and/or faulty construction would be a good second hypothesis as the cause of the failure.
Inadequate maintenance could be a third, particularly if coupled with inadequate construction. For example, inadequate drainage of corrosive water and exposed, inadequately covered structural steel.
There are many factors that could bring a building down: Corrosion – mentioned above, weather, various aging effects inherent in the choice of materials, original design mistakes – as acknowledged above but unlikely in simple structures, abuse, unexpected loads and external forces.
These items or factors can be divided into two fundamental categories:
- Static load support deficiences, and
- Dynamic load deficiences.
Static loads – weight in laymen’s terms, are the basic weight of the building itself and its contents. A building has to be strong enough to resist gravity and hold itself up. The static loads can be subdivided into two categories:
- Dead loads, and
- Live loads.
Dead loads are loads that never seem to change in a building such as the weight of the floors, walls and roof. Live loads are loads that can sometimes change in a building due to weather, occupancy, or building use. For example, the people, furniture and equipment, and possibly vehicles in a parking garage (see below), etc.
Dynamic loads are loads on a building that change during a relatively short period of time. They are repeatedly applied and released. Dynamic loads are added to the static loads. Typical dynamic loads include strong and variable winds, machinery that pounds or shakes the floors of a building (vehicles in a parking garage?), and earthquakes. Dynamic loads can sometimes cause contruction materials to fail due to fatique.
Any one or more of several factors could have brought the building in Elliot Lake down. For sure, inadequate design of a simple building is a possibility but, based on my experience, inadequate construction and maintenace are more likely causes, and good second hypotheses.
I propose, but who knows until a thorough forensic engineering investigation is carried out?
Reference
James, Stuart H. and Nordby, Jon J., Editors, Forensic Science; An Introduction to Scientific and Investigative Technicques, 2nd ed., Chap. 23, Taylor & Francis 2005